For installing cables, in particular optical cables or optical fibers, in tubes, various techniques are known. The oldest and best-known technique is pulling the cable through the tube. This involves a reel with cable being disposed at the insertion end of a tube and the cable being pulled through the tube by means of a pulling wire priorly provided in the tube. This technique has as a drawback inter alia that the pulling forces required for overcoming the friction of the cable over the often winding tubular path are very high and, in particular with optical fibers or optical cables, can exceed the allowable value.
EP-A-0 108 590 describes a technique for installing optical fibers of a slight diameter in a tube by means of a fluid under pressure. For this purpose, a blowing unit is disposed at the insertion end of the tube. After the leading end of the fiber has been inserted into the tube, the blowing force is sufficient for moving the fiber through the tube.
EP-A-0 292 037 describes an adaptation of this known technique for optical cables having an intrinsic stiffness, with the insertion being effected through a combination of pushing and blowing.
It is also known to install cables in tubes by exerting a suction force on the tube end located opposite the insertion end of the tube and thus suck the cable into the tube. Examples hereof can be found in CH-B-677707, EP-A-0 319 194 and in GB-A-2.152.621, which last-mentioned publication describes an element provided at the insertion end of the cable, which element substantially fills up the tube diameter and enables a more efficient insertion through the prevention of leakage.
None of the above-cited publications mentions anything at all about the problem that it is sometimes desired to remove a cable that is already installed from the tube again. This problem is in fact described in EP-A-0 428 830 and in DE-C-39 37 695.
EP-A-0 428 830 also describes a technique for installing optical fibers or cables in tubes by means of blowing force. The cable to be blown into a tube is included in a storage tube that can be wound up so as to be coil-shaped. One end of the storage tube is connected to the installation tube in which the cable is to be installed, and the other end is connected to a compressor whereby the cable is blown from the storage tube into the installation tube. As an advantage of this technique it is mentioned that the compressor need not be disposed close to the inlet end of the installation tube, and that the cable need not be introduced mechanically into a pressure space. This publication also describes that by means of the compressor it is possible to remove a cable from the installation tube by means of blowing force, for which purpose the compressor is connected to the end of that tube other than the end to which the storage tube is coupled, and the cable is blown out of the installation tube into the storage tube. However, the use of a storage tube has drawbacks in view of the room required therefor and the limited cable length that can be included therein. When a cable is being removed from an installation tube, it is also a drawback that the compressor and the storage tube are located in different places, each at one end of the installation tube, so that two operators are required. Further, for instance during the removal of cables from a star-shaped network, either the compressor or the storage tube should each time be displaced to another end of the star.
DE-C-39 37 695 describes a cable having several optical fibers, which fibers are provided in separate ducts in the cable in such a manner that when the cable is partially cut through and a duct is opened, the fiber present therein can be pulled from the end of the cable remote from the exchange and be used for a house connection. In this manner, from a cable, a large number of branches can be realized at different distances from the exchange. This publication mentions the problem that pulling the fiber from the cable may present problems if the length to be pulled out is great. For that reason, a cable is used wherein the length of twist of the fibers is 0.6-8 m and preferably 5-6 m, i.e. much longer than is usual and desired, and it is further proposed in this publication to lay the fibers in a gel-like substance or to shorten the fibers already in advance. The first proposal increases the cost price, which also holds for the second proposal, which second proposal has the additional drawback that the flexibility for choosing the locations of the branches is restrained already in advance.